This invention relates to a method and composition for treating molten metals and alloys of the iron group with a reactive metal to produce nodular iron and more particularly to the use of low boiling point alkali and alkaline earth reactive metals for treating molten iron and alloys thereof to produce nodular iron and effect desulfurization thereof.
As is well known in the art to which our invention relates, many methods have been proposed for treating molten metals and alloys of the iron group with a reactive metal to produce nodular iron and to desulfurize iron. One method for introducing magnesium into the molten iron has been through the use of an iron, silicon, magnesium alloy. This alloy has been added by placing a cushion of cold metal in the ladle on top of the iron silicon magnesium alloy to minimize the loss of magnesium and contain the volatility within the vessel. This method is disadvantageous when the silicon content of the base metal is high and the addition of more silicon would put the metal out of chemical specification. Accordingly, this method of introducing magnesium into the molten metal is used when a reduced quantity of magnesium is desired to nodularize and when silicon will not create a problem. That is, returns to melt must be closely controlled due to high silicon content of the iron silicon magnesium alloy.
Another method of introducing magnesium into molten iron has been to immerse pure magnesium into the molten iron with a plunging bell within a suitable vessel. This is employed when a large quantity of iron needs to be desulfurized and nodularized. The use of pure magnesium is undesirable because of the fast and violent reaction which takes place when the pure magnesium is immersed in molten iron. Not only does the violent reaction cause a safety hazard but there is a high loss of magnesium due to its volatility. Also, expensive equipment is required to handle the pure magnesium.
Another method of introducing magnesium into molten iron has been through the use of a porous refractory body, such as porous coke and porous graphite, which are impregnated with magnesium. That is, the porous refractory body is dipped in the molten magnesium whereby the magnesium impregnates the porous body. Such a method is disclosed in the Snow U.S. Pat. No. 3,321,304. The porous refractory body impregnated with magnesium is immersed in the molten iron by employing a plunging bell or the like. This method of introducing magnesium into molten iron is employed where a greater quantity of magnesium is needed and no other alloys are desired. This method is also employed when the carbon content in the coke can be advantageous. While the reaction time with this method is very slow, there is a violent reaction upon initially immersing the magnesium impregnated body into the molten iron whereby there is a great loss of magnesium due to volatility. Other disadvantages in this method are that expensive equipment is required to handle the violent reaction and undissolved coke must be skimmed from the ladle.
Another method of introducing magnesium into molten iron is disclosed in the Easwaran et al U.S. Pat. No. 3,902,892. In accordance with this method, a mass of scrap ferrous metal pieces is impregnated with magnesium. This body impregnated with magnesium must also be introduced into the molten iron by use of a plunging bell assembly or the like. This method is employed where a greater quantity of magnesium is desired and the steel turnings contained within the product can be utilized. There are disadvantages in this method due to the fact that a violent reaction occurs when the product is immersed in the molten iron and also expensive equipment is required due to volatility.
In addition to the above methods of introducing magnesium into molten iron, there is a German alloy, "VL 55", which contains approximately 30-35% magnesium along with silicon, rare earth and other ingredients. The product is introduced into the molten iron by employing a plunging bell. This product is employed when a greater quantity of magnesium is desired and where silicon, rare earth and other ingredients are desired. A disadvantage in this method is that a violent reaction occurs when the product is introduced into the molten metal, thereby requiring expensive equipment.
Another method of introducing magnesium into molten iron is by employing the inmold process wherein the magnesium is added to the melt through chambers in the mold gating system rather than in the ladle before the casting is poured. The nodulizing agent is a cast to shape iron, silicon, magnesium alloy or a mechanical mixture of granular ferrosilicon and atomized magnesium formed into pellets. Accordingly, two metallics are combined in pellet form. This latter process is mentioned in "NEWSLETTER" published by The National Magnesium Association, May 1978, page 5. This publication mentions other attempts to use elemental magnesium by means, such as pneumatic injection, refractory coatings, external magnesium vaporizers, special pockets in refractory-lined reactor vessels, and pressure treatment systems. The refractory coatings heretofore employed have been merely external coats applied to solid lumps of magnesium, such as a dip-wash coat or a coat applied in accordance with the Snow U.S. Pat. No. 3,321,304, mentioned above.